Gerald Wiener

A comparison of the body size, fleece weight and maternal performance of five breeds of sheep kept in one environment.

Female sheep of five breeds (Scottish Blackface (B), South Country Cheviot (C), Welsh Mountain (W), Lincoln Longwool (L), and Southdown (S)) were purchased as lambs of 5–6 months old and subsequently kept as a single flock on a grassland farm until they were 4½ years old (Southdowns to 3½ years). The sheep were used in a crossbreeding experiment with up to six breeds of ram. The sheep were weighed and 8 body parts measured at frequent and regular intervals. The Blackfaces and Southdowns grew, relative to their mature size, a little faster initially than the Cheviots. Mature weights (lb.) were approximately B: 146, C: 145, W: 101, L: 197 and S: 129. The breeds differed in conformation but the order of maturity of the body parts was the same for each breed. Variances for body measurements decreased slightly with increasing age for early-maturing parts and increased a little for later parts. The coefficients of variation decreased slightly with increasing age. Variance in weight increased markedly with age (but not the C.V.) and showed the only large breed differences in variance. Fleece weight, after the first shearing, was strongly affected by the amount of wool shed prior to shearing. Shedding differed significantly between the breeds, Cheviots shedding most. Shedding was also related to the number of lambs born per ewe. The total weights (lb.) of wool produced from four shearings were B: 23·2, C: 20·0, W: 15·6, L: 55·5 and S (estimated from 3 shearings): 20·8. The numbers of lambs born per ewe totalled over three lamb crops were B: 5·81, C: 5·21, W: 4·53, L: 4·85 and S (estimated from two crops): 4·55. In survival to weaning, single-born lambs were no better than twins and crossbred lambs no better than purebred. Lambs born to Welsh mothers had the best survival; the other breeds did not differ significantly from each other. The breeds of ewe differed in the proportions of their twin lambs which had to be assisted at, or soon after, birth. When each breed of ewe was mated to the same breeds of ram, the weights of lambs born to Blackface mothers did not differ significantly at birth from those of lambs born to Cheviots but were heavier at weaning. Lambs from Welsh mothers were the lightest at birth and weaning. In relation to (live-weight) 0·73 the maternal performance of the Welsh females was at least as good as that of the Blackfaces but the wool production was slightly poorer.

Body size and conformation in sheep from birth to maturity as affected by breed, crossbreeding, maternal and other factors

Body weight was studied from birth to 5½ years of age and six linear measures of body size from birth to 4¼ years for sheep of five breeds, Scottish Blackface, Cheviot, Welsh Mountain, Lincoln Longwool and Southdown, and of crosses of these breeds with each other and with the Tasmanian Merino, but not in all possible combinations. The sheep were run as a single flock. Numbers ranged from 753 at birth to 150 at the end of the experimental period. There were marked differences among the breeds and crosses in all aspects of body size and some differences in rate of maturity. They also differed in conformation independently of body weight. Crosses of the hill breeds with the Lincoln and probably with the Southdown were heavier than the average of the parental breeds and larger in some linear body measurements from about weaning onwards. The weights of crosses of Blackface and Cheviot with Lincoln eventually exceeded those of the heavier parent of the cross. For the crosses among the three hill breeds only the Blackface Cheviot cross showed significant deviations from mid-parent values for weight and size. Maternal effects were important for all traits studied from birth to weaning and for weight up to a year old. In relation to mature size, Welsh dams produced the biggest and Lincoln the smallest lambs. The data did not permit Southdown maternal effects to be estimated. The effects of birth type and rearing were apparent for late maturing body parts up to a year old and for weight up to 3 years. Males, measured only from birth to weaning, were heavier and generally larger than females. Residual correlations between the various measures of size varied from 0·1 to 0·7.

Maternal performance in sheep as affected by breed, crossbreeding and other factors

Maternal performance of female sheep of three hill breeds, Scottish Blackface, Cheviot and Welsh Mountain, and the crosses among these breeds has been studied in terms of lifetime production and some of its components. The data are based on 193 ewes, which were given the opportunity of having four annual lamb crops, and their lambs. There was no significant variation among the breeds and crosses in ewe survival or in the proportion of barren ewes at each lambing. There was significant variation among the breeds and crosses in the number of lambs born per ewe lambing, in lamb survival and in weights of lamb at birth and at weaning. Crossbred ewes (producing crossbred lambs) had more and heavier lambs than expected from the average of the pure breeds contributing to each cross, but the three crossbred types differed in the amount of heterosis shown. Over their lifetime in the flock there were significant breed differences in the total weight of lambs weaned, with crossbred ewes producing about 9% more than the average of the parent breeds involved. The crossbred ewes produced more weight of lambs over their lifetime than pure Cheviot or pure Welsh Mountain ewes, but not as much as pure Scottish Blackface. Effects of parity of dam and of sex, birth type, and type of rearing of lamb are given.

Factors influencing average milk yield of herds at two levels of production.

An experiment was started in 1950 designed to find out what proportion of the difference in milk yield between herds is genetic in origin. Sixty-five pairs of twins were split at birth equally between farms having high-yielding herds and farms having low-yielding herds. A previous paper on this experiment reported on the growth of the twins, the present paper on milk yield and on management practices in the herds. Twenty-four pairs of twins survived to complete one lactation and these provide an estimate of 24%±18% for the genetic part of the difference between the herds. Aspects of rearing of the twins and of management of the herds were examined. Twins in the high-yielding herds were served and calved earlier than those in the low-yielding group but they had a longer interval between service and calving. Differences between average heifer yields and average cow yields were from one-and-a-half to two times greater in the high- than in the low-yielding herd group. There were no obvious quantitative differences in feeding practice between the two groups although differences in body size suggest that twins in the high group were done better. For the age at first service there was a positive rank correlation of 0·30 between body size differences and subsequent differences in first lactation milk yield. There was no single factor of management or environment which appeared to be the cause of the yield difference between the herds.

Effects of crossbreeding and inbreeding on the frequencies of blood groups in three breeds of sheep

Blood groups were determined for eight loci in a total of 742 sheep and for the Tf (transferrin) locus of 512 sheep comprising the Scottish Blackface, the Cheviot and the Welsh Mountain breeds and their crosses. Each breed and cross was represented by a non-inbred F 2 generation and by three stages of inbreeding (25, 37½ and 50%). The loci for which all genotypes were distinguished were Hb, M, and Tf, and those for which partial description (including the recessive homozygote) was made were A, B, C, D, R and i. There were large differences among the three pure breeds only for the frequencies at the Hb and Tf loci. The homozygote frequencies of the Blackface-Welsh and Cheviot-Welsh crosses were approximately half-way between their respective pure breeds. For the Blackface-Cheviot cross the homozygote frequency was considerably lower than either parental breed, suggesting that over all loci there were greater differences in gene frequencies between these two breeds than between the Blackface and Welsh or Cheviot and Welsh. On average over all loci (except Tf) inbreeding had the effect of decreasing heterozygosity roughly in relation to expectation. Individually this effect was statistically significant only for ii, M b M b , Hb A Hb A and Hb b Hb b . For the Tf locus there was no average decrease in heterozygosity as a result of 25% inbreeding but thereafter there was a greater decrease in the purebreds than in the crosses. There were small ( ii blood types and genotypes at several other loci, and between dd and the M system genotypes.

An association between the concentration of copper in whole blood and haemoglobin type in sheep

In a genetically diverse flock of about 320 sheep a significant association has been found between the concentration of copper in whole blood and the haemoglobin type. Sheep were bled on four occasions over a period of 1 year, with the flock mean concentration of copper varying between 53 and 96 fig per 100 ml whole blood. The copper concentrations in whole blood from sheep of haemoglobin type B exceeded those from sheep of type A by 9, 16, 15 and 15 fig per 100 ml on the four occasions respectively. The copper concentrations from sheep of type AB were 8, 11, 7 and 7 μg higher than those from type A. Differences in the frequency of the three haemoglobin phenotypes accounted for part of the breed variation in copper concentration previously observed in the same flock, but even when that effect was allowed for, highly significant breed variation remained. When plasma instead of whole blood was examined in two other flocks from which breed variation in plasma copper concentration had been reported no association was found between the plasma copper concentration and haemoglobin type.

Selection for plasma copper concentrations within haemoglobin type in sheep

From among 27 rams of haemoglobin type A the two rams with the highest plasma copper concentration and the two rams with the lowest were selected on the basis of a single determination. In the same way four rams were selected from among the 29 rams of haemoglobin type B. The average difference between the ‘high’ and the ‘low’ rams was 103 μg copper per 100 ml plasma. The rams were mated to 105 unselected females. Lambs born as a result of these matings were blood-sampled on eight occasions from 3 weeks to 29 weeks of age. The plasma copper levels of the lambs sired by the ‘high’ copper rams were higher on average than those sired by ‘low’ copper rams. The two groups diverged from 12 weeks of age onward to a maximum difference, at 29 weeks, of 18 μg copper per 100 ml plasma. There was also an initial difference of 13 μg at 3 weeks but a much smaller one at 6 and 9 weeks. There was no corresponding difference in plasma copper concentration between the offspring of haemoglobin A and haemoglobin B rams. The results are therefore consistent with the hypothesis that the association previously observed in the same flock between haemo-globin type and plasma copper level is unlikely to be due to an effect of the gene controlling haemoglobin type, but could be due effectively to a linked ‘copper gene’. Correlations between maternal plasma copper concentration 3 weeks after parturition and lambs plasma copper level showed a marked decline as the lambs grew older, starting from around 0·6 at 3 or 6 weeks old. This suggests a maternal ‘environmental’ influence on lambs plasma copper in addition to any genetic effects.